Safety Issue
An extended time in service in the 'A' windscreen filter
location appeared to increase the risk of an electrical arcing
event in that filter.
Aircraft manufacturer comment
In its consideration of alternate strategies to address the
failure of the aircraft's 'A' windscreen electrostatic filter, the
aircraft manufacturer determined that there was no apparent trend
in relation to the age of the failed filters. Similarly, the
manufacturer considered that the failure condition was not
predictable, and therefore placing a life on the filters was not
practicable.
Additional aircraft manufacturer comment
In its response to the draft safety action that was proposed by
the ATSB, the aircraft manufacturer advised that, in accordance
with its procedures, the classification of the event was 'MAJOR'
but that, given the total flight hours of the BAE 146/RJ of over 10
million hours, the electrostatic filter failure rates were 'within
acceptable levels for this failure classification.' In regard to
the possibly age-related nature of the 'A' windscreen electrostatic
filter failures, the manufacturer noted that, although the first
aircraft was delivered in 1986, the failures were confined to units
that were manufactured in or after 1987.
Component manufacturer
The manufacturer of the electrostatic filter believed that the
'A' windscreen electrostatic filters became susceptible to failure
after extended periods in service in the moisture-laden environment
associated with that filter's location. Advice was provided by the
manufacturer that 'the unit's location in the aircraft may generate
a combination of environmental factors detrimental to the unit's
service life.'
Additional component manufacturer comment
In its response to the draft safety action that was proposed by
the ATSB, the component manufacturer advised that, in its opinion,
placing a time in service limit on 'A' windscreen filters 'would be
the most prudent action to avoid repeat incidences similar to that
contained in the report'.
In addition, the component manufacturer carried out an examination
of its internal design and drawing modifications records for the
electrostatic windscreen filter, including since the inception of
the BAe 146 aircraft. That examination found no correlation between
any design or production changes to the electrostatic filter and
the late 1980s period.
ATSB comment
Despite the disparity in the aircraft and component
manufacturers' conclusions with regard to the influence of 'A'
windscreen electrostatic filter time in service on the risk of an
electrical arcing event in that filter, an extended time in service
in the 'A' filter location appeared to increase that risk.
Whereas, to date, the existing engineering and other defences had
minimised the consequences of electrical arcing events in the 'A'
windscreen electrostatic filter, it appears that there may be an
opportunity to reduce the likelihood of future electrical arcing
events in those filters as a result of the consideration of an
appropriate time in service for filters in that location.
Safety Recommendation
The Australian Transport Safety Bureau recommends that GKN
Aerospace, in conjunction with BAE SYSTEMS, address this safety
issue.
